Police and firefighters conducted on-the-spot investigations Wednesday of Bridgestone Corp.'s tire plant on suspicion of professional negligence over a major fire there earlier this week.
The blaze, which broke out around noon Monday at the tire maker's Tochigi plant in Kuroiso, Tochigi Prefecture, was finally brought under control at 10:30 a.m. Wednesday after destroying more 100,000 tires and forcing some 5,000 nearby residents to be evacuated.
The probe is being conducted by the Tochigi Prefectural Police, the Tokyo Fire Department and local firefighters.
The police suspect that professional negligence is behind the fire, according to police sources.
Inspections are focused on one of eight mixing machines in the facility. According to witness testimonies, the fire apparently started in one machine -- the No. 3 rubber mixer -- and ignited nearby flammable foam materials, the police said. Wednesday's probe found that most damage was in the vicinity of this machine.
According to investigative sources, it was discovered that unlike other parts, the motor of the No. 3 mixer had not been changed for some 30 years.
The No. 3 mixer, installed in 1974, was taken apart for maintenance in 1998. Parts vulnerable to wear, such as the rotor, were exchanged om a regular basis, the sources said.